The invention relates to a crankshaft bearing for internal combustion engines provided with a light metal alloy engine housing.
The amount of bearing play in internal combustion engine crankshaft bearings has a significant influence on the development and transmission of noise; it also influences the flow of lubricating oil through the bearing. Considerable increases in bearing play with rising temperature occur particularly in those internal combustion engines that have a housing made of a light metal alloy, whose crankshaft bearings receive a ferrous metal crankshaft. The different coefficients of expansion of light metal housings and ferrous metal crankshafts, depending on the temperature, cause the bearing bore of the respecting crankshaft bearing to increase, resulting in increased noise during engine operation.
To avoid this disadvantage, German Patent Document DE-OS 31 35 683 teaches casting a ferrous metal core in a bearing cover of a crankshaft bearing made of a light metal alloy, said core being formed by a strip extending transversely to the bearing cover and at a distance from the crankshaft journal. Since in this design the bore of the bearing cover expands as before, the desired noise reduction is not achieved with the means proposed.
In another known bearing for the crankshaft, disclosed in German Patent Document DE-34 26 208 C1, good results regarding noise reduction are achieved in a housing made of a light metal alloy; wherein the ferrous metal core cast in the light metal crankshaft bearing surrounds the crankshaft journal so that undesired increases in bearing play are avoided.
An object of the invention is to improve further a crankshaft bearing of an internal combustion engine with a housing made of a light metal alloy, for the specific purpose of simplifying a highly effective device for reducing bearing play and reducing its manufacturing cost.
According to the invention this goal is achieved by providing a device for reducing the increase in bearing play during operation of the engine, wherein the device is provided between a crankshaft journal and a bearing bore and includes an annular compensating element surrounding the crankshaft journal, said compensating element being made of a material with a relatively high coefficient of thermal expansion.
The primary advantages achieved with the invention consist in the fact that the device comprises a compensating element located between the bearing bore and the crankshaft journal and has a much greater coefficient of expansion than its adjacent parts, so that the increase in bearing play during operation of the engine, due in particular to the engine housing being made of a light metal alloy, can be deliberately minimized. In addition, oil flow is influenced favorably because the oil film in the bearing bore exhibits improved bearing capacity.
In order to ensure correctly functioning running properties for the crankshaft or its journal, a bearing shell made of a metallic material, steel for example, is provided between the compensating element and the crankshaft. To the extent that comparable running properties can be achieved, however, another design, for example a compensating element with a foil or the like, is also possible.
Plastic, especially high-strength thermosetting plastic, polyamide for example, is considered an especially favorable material for the compensating element. In addition, an anisotropic material must meet the requirements for the compensating element, with this material exhibiting thermal expansion that is relatively great in the radial direction and slight in the axial and tangential directions. Zinc or a zinc alloy can also possibly serve as a material for the compensating element.
The compensating element and the bearing shell form a module that can be manufactured and/or assembled from supplier parts in simple fashion and installed in the crankshaft bearing when the engine is assembled. The compensating element can be held in position by a positive fit of the bearing shell, which is U-shaped in cross section, but other configurations with a positive action are also possible. One variation involves the compensating element being connected with the bearing shell by gluing, vulcanizing, or the like. Another embodiment is one in which the compensating element is physically connected by gluing or vulcanizing with the bearing bore.
The compensating element, for example with the bearing shell as a module, is not only suitable for one-piece crankshaft bearings like those used in one-cylinder engines, but also for divided crankshaft bearings composed of a housing section of a cylinder crankcase, also called a bearing seat, and a bearing cover, e.g. a bearing bridge or a crankcase bottom. In this case the device composed of the compensating element and the bearing shell is formed by two shell-type halves inserted in the bearing bore.
Finally, the device is suitable for mounting crankshafts not only in internal combustion engines with pistons, but in piston compressors as well.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.